supramolecular coordination chemistry · 2015. 9. 3. · supramolecular chemistry. the review...

Supramolecular coordination chemistry

Chullikkattil P. Pradeep and Leroy Cronin*DOI: 10.1039/b612867j

This Chapter reviews the literature reported during 2006 in the field ofSupramolecular Chemistry. The review focuses on the design, synthesis andself-assembly of metal-based units leading to the construction of metallo-supramolecular architectures.

Highlights

Highlights include the synthesis and structural characterisation of Chiral Borrome-

ates, knots that are characterized by the Brunnian link,4 the formation of 1D

luminescent inorganic micro- and nano-wires directed by PtII� � �PtII interactions,15and the self assembly and crystallization of giant polyoxometalates, comprising both

wheel shaped and hollow, spherical structures. These are combined together leading

to a single mesoscopic molecule.64 The direct crystallographic observation of the

in situ generated Cp0Mn(CO)2 (Cp0 = methylcyclopentadienyl) 16 electron unsatu-

rated complex by photodissociation of Cp0Mn(CO)3 in a self assembled coordina-

tion cage has been achieved and shows that the geometry of an unsaturated 16

electron transition metal centre adopts a pyramidal geometry.68

1. Introduction and scope

This report focuses on the development in design, synthesis and self-assembly of

metal-based architectures and ligands designed to aid the construction of metallo-

supramolecular architectures. As was the case last year, the degree of selectivity

applied when compiling this account is, therefore, very high although we have

attempted to summarise some of the most important developments. Several crystal

structures have been included in this report to aid visualisation and conceptualisa-

tion of the many interesting architectures that have been characterised. For ease of

representation and understanding a common colour scheme/size scheme is used in all

the structural figures unless otherwise stated; the carbon atoms are light grey,

nitrogen atoms white, metal ions large black spheres, sulfur atoms large grey

spheres, oxygen or phosphorus atoms are small black spheres.

2. Metallomacrocycles

A new ditopic triphenylamine-based bis(terpyridine) ligand 4,40-bis(2,20:60,200-ter-

pyridinyl)triphenylamine (L1) possessing the disubstituted triphenylamine unit as an

angle-control element, which can form hexagonal metallomacrocycles, has been

synthesized. This ligand system is found to form a unique hexagonal metallomacro-

cycle family [Fe6(L1)6(PF6)12] and [Zn6(L1)6(BF4)12], utilizing terpyridine–metal(II)–

terpyridine connectivity. The structures of the ligand and the corresponding

Department of Chemistry, The University of Glasgow, University Avenue, Glasgow,UK G12 8QQ

Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 287–332 | 287

This journal is �c The Royal Society of Chemistry 2007

REVIEW www.rsc.org/annrepa | Annual Reports A

metallomacrocycles were confirmed by means of 1H and 13C NMR, UV-Vis

spectroscopy and mass spectrometry. Crystal structure analysis of the ligand L1

shows that the angle between the two terpyridinyl moieties is 119.691, which enables

the formation of the hexagonal-shaped metallomacrocycles.1

The thiophene-based bis(N-methylamidopyridine) ligand SC4H2-2,5-{C(QO)-

N(Me)-4-C5H4N}2 (L2) has been found to react with silver(I) salts (AgX) to form

1:1 macrocyclic complexes [Ag2{L2-A}2][X]2 in the solid state, which have the cis

conformation of the C(QO)N(Me) groups when XQCF3CO2, NO3, or CF3SO3 (see

Fig. 1 for one example) but as the polymeric complex [Agn{L2-B}n][X]n, with the

unusual trans conformation of the C(QO)N(Me) groups, when X = PF6. The

macrocyclic complexes reported with this ligand are found to contain transannular

argentophilic secondary bonds.2

The arene-linked bis(pyrazolyl)methane ligands m-bis[bis(1-pyrazolyl)methyl]-

benzene, (m-[CH(pz)2]2C6H4, L3), p-bis[bis(1-pyrazolyl)methyl]benzene, (p-[CH(pz)2]2-

C6H4, L4), and 1,3,5-tris[bis(1-pyrazolyl)methyl]benzene (1,3,5-[CH(pz)2]3C6H3, L5)

are found to react with AgX salts (pz = 1-pyrazolyl; X = BF4� or PF6

�) to form

silver(I) complexes. Two types of molecular motifs are formed depending on the

arrangement of the ligating sites about the central arene ring. Reactions of the m-

phenylene linked L3 with AgBF4 and AgPF6 afford complexes consisting of discrete,

metallacyclic dications: [Ag2(m-L3)2](BF4)2 and [Ag2(m-L3)2](PF6)2, but when the p-

phenylene-linked L4 is treated with AgBF4 and AgPF6, acyclic, cationic coordina-

tion polymers are obtained: {[Ag(m-L4)]BF4}N and {[Ag(m-L4)]PF6}N. However,

reaction of L5, containing three bis(pyrazolyl)methane units in a meta arrangement,

with an equimolar amount of AgBF4 again yields discrete metallacyclic dications in

288 | Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 287–332


which one bis(pyrazolyl)methane unit on each ligand remains uncomplexed: [Ag2-

(m-L5)2](BF4)2. Treatment of L5 with an excess of AgBF4 affords a polymer of

metallacycles, {[Ag3(m-L5)2](BF4)3}N. On the whole the supramolecular structures

of the silver(I) complexes are organized by noncovalent interactions, including weak

hydrogen bonding, p–p, and anion–p interactions.3

Two pairs of enantiomerically related Borromeates were synthesized stereospeci-

fically from enantiomeric phenylglycine derivatives using Zn2+ ions to template their

formation. All four optically active compounds have three macrocycles each

containing four stereogenic centres. The one example whose crystal structure has

been determined adopts an asymmetric conformation. Furthermore, the Zn2+

octahedra, found in the X-ray crystal structure, deviate substantially from ideal

geometry, suggesting that chirality is being transferred efficiently from the 12

stereogenic centres to the six Zn2+ centres. Also in the chiral Borromean rings,

the expected C3 axis was not present, the symmetry is reduced to C1 on account of

one of the three macrocycles adopting a flipped chair-like conformation.4

A supramolecular approach to metalloenzyme models in aqueous solution based

on the dynamic self-assembly between macrocyclic hosts with cation receptor

properties, organic guests, and metal ions is reported. In this study calixarenes were

employed as hosts, bicyclic azoalkanes (L6, L7, L8) in particular 2,3-diazabi-

cyclo[2.2.2]oct-2-ene (L6), as ideal guest molecules. Upon addition of transition

metals (e.g., Zn2+, Co2+, Mn2+), a hypsochromic shift was observed, which signals

Fig. 1 A view of the structure of the macrocyclic trifluoroacetate complex [Ag2(CF3CO2)2-

{L2-A)2}2]



the formation of a ternary complex in which the azo group functions as a

monodentate ligand.

In the resulting ternary complex, the guest is held in place by hydrophobic

interactions with the host, while the metal ion experiences attractive Coulombic

interactions with the negative charges positioned at the portal of the macrocycle. It

was found that only in the presence of the macrocyclic host will the guest and metal

form the desired complex, that is, the host assists or ‘‘templates’’ the formation of the

metal–ligand bond. The host brings two species together to form a metal–ligand

complex which, in the absence of host, is not present in significant amounts because

of low bimolecular affinity. Conceptually, the phenomenon of host-assisted metal–

ligand bond formation stands out, as well as the high selectivity for the formation of

a ternary complex. This strategy results in an interesting interplay between co-

operative and competitive binding arising from a triple supramolecular recognition

motif.5

Kinetically-locked, metallomacrocycles incorporating adenine based ligands have

been synthesised through self-assembly using a [RuII([9]aneS3)] templating moiety

and the formation of macrocyclic trimers has been evidenced from NMR and FAB-

MS spectrometry studies. Also it was found that, for suitably hindered adenine

derivatives the synthetic procedure appears to be general.6

A general strategy for the construction of nanoscopic and mesoscopic functional

supramolecular architectures of controllable size, chirality, and functionality has

been reported. Described include the expeditious stepwise directed assembly of large

homochiral metallocycles with up to 38 6,60-bis(alkynyl)-1,10-binaphthalene brid-

ging ligands (L) and 38 trans-Pt(PEt3)2 ([Pt]) centres and with cavities as large as

22 nm in diameter. These unprecedented mesoscopic metallocycles are synthesized

by cyclization of different lengths of oligomeric building blocks, Lm[Pt]m+1Cl2 (m=

1, 2, 3, 5, 7, 11, 19, and 31) and [Pt]nLn+1H2 (n= 1, 2, 3, 4, 5, 6, 10, 18, and 30), (see

Scheme 1) and have been characterized by a variety of techniques. The extension of

this methodology to the synthesis of non-homochiral metallocycles of diverse

topologies and macrocyclic structures is also possible.7

3. Grids

A compartmentalized {4 � [2 � 2]} Mn(II)16 antiferromagnetically coupled square

grid [Mn16(L9)8(OH)8](NO3)8 has been reported from the self-assembly reaction of a

tetratopic pyridazine bis(hydrazone) ligand (L9) and Mn(II). Fig. 2 shows the core

structure of this molecule.



Scheme 1

Fig. 2 Core structure of the square grid molecule [Mn16(L9)8(OH)8](NO3)8.



The tetratopic bis(hydrazone) ligand L9 has two pairs of coordination pockets,

arranged on either side of a central pyridazine group, which can bind to four metal

ions. However, the bend in the ligand structure was considered to be a possible

impediment for self-assembly to form a [4 � 4] M16 grid.8 Reversible conversion of a

grid-like into a pincer-like complex modulated by the nature of the solvent has been

reported. The triazine derived ligand L10 reacts with one equivalent of Co2+ salts to

give complexes whose architecture were found to depend on the solvent employed:

the [2 � 2]-grid like tetranuclear complex and the pincer-like mononuclear complex,

obtained respectively by crystallization from nitromethane and from acetonitrile,

may be inter-converted reversibly, the grid-pincer conversion being markedly

accelerated by adding an amine.9

From single crystal measurements, a metamagnetic-like behaviour in supramole-

cular [2 � 2] grid molecules of general formula [CoII4(L11–L13)4]8+, with bis(bipyr-

idyl)pyrimidine-based ligands L11–L13, was demonstrated. The magnetization

curves exhibit metamagnetic-like behaviour and are explained by the weak-exchange

limit of a minimal spin Hamiltonian including Heisenberg exchange, easy-axis ligand

fields, and the Zeeman term. It is also shown that the magnetic coupling strength can

be varied by the substituent R1 in the two-position on the central pyrimidine group

of the ligand L.10

The interaction of appropriate metal ions (Pb2+, Zn2+) with helical ligand

strands, obtained by hydrazone polycondensation, generates polymetallic supra-

molecular architectures of rack and grid types, by uncoiling of the ligand. The

interconversion between the helical free ligand and the linearly extended ligand in

the complexes produces reversible ion-induced, nanomechanical molecular motions

of large amplitude. It has been integrated in an acid–base neutralisation fuelled

process, which links the extension/contraction of the ligand strands to alternating

changes in pH.11



4. Cylinders, rings and squares

A di-cationic dicopper(I) metallosupramolecular cylinder is prepared from pyridyl-

imine-based ligand L14. DNA binding studies showed that this cylinder binds more

strongly to DNA than the spherical dication [Ru(phen)3]2+ (phen = 1,10-phenan-

throline) showing potential for the design of supramolecular arrays with size and

shape similar to DNA recognition motifs over small molecular units.

This copper cylinder also exhibits interesting DNA-cleavage activity in the

presence of peroxide. The cylinder exhibits an unusual tendency to perform a

double-strand cleavage at the same site. The cleavage ability extends the potential

applications of these metallosupramolecular cylinders, opening up the possibility of

using copper-based cylinders as artificial nucleases.12

The construction of Cu2+-containing 1 D supramolecular chains is achieved by

the reaction of bifunctional organic ligands L15, L16, L17 and L18 with dinuclear

Cu2+ acetate or Cu(II) 2-fluorobenzoate complex ions. L15–L18 contain a metal-

coordinating pyridyl site and a self-complementary hydrogen-bonding moiety. The

structures of the complexes formed with copper(II) display a ‘‘paddlewheel’’ ar-

rangement, with four carboxylate ligands occupying the equatorial sites, leaving

room for the bifunctional ligand to coordinate in the axial positions and the

structure of one such complex is shown in Fig. 3. The self assembly process, which

organizes the coordination-complexes into the desired infinite 1-D chains, is driven

by a combination of N–H� � �N and N–H� � �O hydrogen–bonds in five of the seven

structures.13

The reaction of chelating conjugated Schiff-base macrocyclic ligands L19–L21

with Zn(OAc)2 gives bowl-shaped heptanuclear Zn complexes featuring Zn in



tetrahedral, octahedral, and square-pyramidal geometries. Structural and solution

studies indicate that vacant Zn coordination sites within the bowl may be accessed,

suggesting that these coordination complexes may be used as mimics for Zn fingers

and hydrolytic ZnII-containing enzymes.14

1D luminescent inorganic micro and nanowires from [Pt(CNtBu)2(CN)2] that are

aggregated and directed by PtII� � �PtII interactions has been reported. The precursor

[Pt(CNtBu)2(CN)2] was synthesized in high yield by stirring K2PtCl4 and excess tert-

butyl isocyanide in water at room temperature. This is interesting since weak

PtII� � �PtII interactions provide a bonding influence for the construction of 1D

chains. More importantly, PtII� � �PtII interactions not only induce the formation of

1D nanostructures but are also responsible for the intense green 3[5ds*,6ps] emission

of the self assembled [Pt(CNtBu)2(CN)2]wires.15

Fig. 3 Basic structure of the copper complex containing the ligand L15.



The metal-ion-directed supramolecular self-assembly of the perylene bisimide

building block L22 leads to a square array as shown in Scheme 2 which incorporates

four inner perylene bisimide dyes and sixteen aminonaphthalimide antenna dyes.

The optical and photophysical properties of aminonaphthalimide-functionalized

perylene bisimide ligand L22 and square array were investigated in detail.16

Scheme 2



5. Frameworks

The expansion of the rectangular cavities (RCs) is achieved by replacing bridging

isonicotinic acids L23 with longer 4-pyridyl-substituted carboxylic acids (PCA). For

this purpose, the following PCAs have been employed: trans-3-(4-pyridyl)propenoic

acid (acrylH) L24, 4-(4-pyridyl)benzoic acid (pybenH) L25, and trans-3-

(4-(4-pyridyl)phenyl)propenoic acid (pppeH) L26. Self-assembly of Ni2+, SCN�,

and each of four PCAs involving isoH, acrylH, pybenH, and pppeH in the presence

of an aromatic guest gives rise to inclusion compounds of the form:

[Ni(SCN)2(isoH)2] � 1/2(benz[a]anthracene), [Ni(SCN)2(acrylH)2] � 1/2(benz[a]-anthracene), [Ni(SCN)2(pybenH)2] � (pyrene), and [Ni(SCN)2(pppeH)2]3/2 � (benz[a]-anthracene). The crystal structures show layered 2D grid-type coordination frame-

works (2D host layers) framed with bridging ligands of the corresponding PCA

dimers and 1D chains consisting of Ni2+ ions and m1,3-SCN�ions. The lengths of the

PCA dimers are 12.269(5) A (isoH dimer), 16.890(4) A (acrylH dimer), 20.89(2) A

(pybenH dimer), 25.387(3) A (pppeH dimer A), and 25.527(4) A (pppeH dimer B).

Each 2D host layer has RCs defined by the two corresponding PCA dimers and the

two SCN bridges. The dimensions of the RCs are expanded in proportion to the

increase in the lengths of the PCA dimers and reflect the number of aromatic guests

that can be included in the RCs.17

The trapping and dilution of the photosensitizer-dye cation [Cu(dmp)2]+ (dmp =

2,9-dimethyl-1,10-phenanthroline) in eight different anionic frameworks formed by

resorcinerenes, poly(hydroxyphenyl) compounds, and fully saturated cyclohexane-

tricarboxylic acid (L27–L33) has been reported.18 The photophysical properties of

the new phases are strongly affected by the electronic structure of the framework

components. The use of saturated frameworks leads to optimization of excited-state



lifetimes of the guest molecules which means that host–guest solids can be designed

so as to optimize the desired photophysical properties.

The synthesis and properties of a robust metal organic framework compound

{[Zn2(L34)] � 4H2O}N, prepared by hydrothermal reaction of ZnCl2 and 4,40-bipyr-

idine-2,6,20,60-tetracarboxylic acid (H4L34) is described and the structure of frame-

work has an unusual 5-connected network with a 4466 topology comprising Zn2+

bound to (L34)4�. The water molecules in the newly-prepared material can be

dehydrated simply by heating the sample in vacuum to yield [Zn2(L34)]N and this

resulting porous material is found to be of high thermal stability, robust and

chemically inert.19

New heterometallic metal-organic frameworks (MOFs) based on tris(dipyrrinato)

metalloligands M(L35)3, M(L36)3, M(L37)3, where M = Fe, Co and Ag salts, are

reported. These were prepared systematically to examine the effects of the core metal

ion, counteranion, and ligand structure on the topology of the resultant network.



The effect of the metal ion (Fe3+ vs. Co3+) on MOF structure was generally found

to be negligible, thereby permitting the facile synthesis of trimetallic Fe/Co/Ag

networks. However, the choice of anion was found to have a pronounced effect on

the MOF topology. Networks prepared with salts of AgO3SCF3 and AgBF4 reliably

formed three-dimensional (10,3) nets, whereas use of AgPF6 and AgSbF6 produced

two-dimensional (6,3) honeycomb nets. The topology generated upon formation of

the MOF was found to be robust in certain cases, as demonstrated by anion-

exchange experiments, and anion exchange was confirmed by X-ray crystallography

in a set of single-crystal-to-single-crystal transformations. This implies that the

coordinative ability of the anion does not play a significant role in the observed

templating effect but changes in the length of the tris(dipyrrinato) metalloligand

were found to override the anion templating effect, resulting exclusively in two-

dimensional (6,3) nets.20

Hydrothermal reactions of lanthanide(III) salts with m-sulfonatephenylphospho-

nic acid (spa) (H3spa) and 1,10-phenanthroline (phen) or N,N0-piperazinebis(methy-

lenephosphonic acid) (ppza) yields six novel lanthanide(III) sulfonate-phosphonates

based on tetranuclear clusters, namely, [La2(spa)2(phen)4(H2O], [Ln2(spa)2-

(phen)2(H2O)5] (Ln = Nd, Eu, Er), and [Ln2(Hspa)(H2ppza)2(H2O)4] (Ln = La

and Nd). These compounds represent the first examples of lanthanide(III)

complexes of sulfonate-phosphonate ligands. More interestingly, they display

isolated, 1D and 3D structures based on two types of tetranuclear lanthanide

units. The dimension of the structure is controlled by mainly the lanthanide ionic

size, the binding modes of the sulfonatephosphonate ligand, and the second metal

linker.21

A new synthetic route to cyclic nickel thiolate complexes using stepwise introduc-

tion of two kinds of thiolate ligands to Ni2+ center has been reported. In this

approach, two different thiolate bridges, namely an alkylthiolate ligand (SiPr or

StBu) and 2-methylthioethanethiolate (mtet) have been used and the use of

these ligands resulted in the selective formation of cyclo-[{Ni(m-SiPr)(mtet)}6] and

cyclo-[{Ni(m-StBu)(m-mtet)}10]. Structure of a benzene included complex [C6H6 C



{Ni(m-StBu)(m-mtet)}10] � 2C6H6 derived from (StBu) is given in Fig. 4. It was found

that the ring configuration of the decanuclear nickel cluster is flexible and exhibits

either a circular or ellipsoidal form which is dependent on the presence or absence of

an encapsulated guest molecule.22

A multifunctional large-pore metal organic open-framework complex

[Cd11(m4-HCOO)6(bpdc)9] � 9DMF � 6H2O (H2bpdc = 4,40-biphenyldicarboxylic

acid), which contains the largest known CdII–carboxylate cluster SBUs (secondary

building units) and has a rare bcu topology has been synthesized by utilizing a

flexible organic acid (HCOOH) as a strong bridging ligand. The CdII-centered

octahedra are linked together by 18 carboxylate groups from bpdc anions, which

bind in a bidentate or a chelating/bridging bidentate fashion, and six m4-HCOO�

moieties to build up a nanosized undecanuclear {Cd11(m4-HCOO)6(CO2)18} cluster

with C3 symmetry. These undecametallic clusters, which behave as SBUs, are

interconnected through the biphenyl groups of bpdc molecules to generate an

extended 3D framework.23 The transformation of a low dimensional framework

to a high dimensional architecture based on different metal ions have been demon-

strated by five novel metal pamidronates (3-ammonium-1-hydroxypropylidene-1,1-

bisphosphonate, APD) formulated as Ni2(C3NH10P2O7)4 � 4H2O, M(C3NH9P2O7) �H2O (M = Co, Mn, Zn) and Cu3(C3NH8P2O7)2 � 2H2O. Their structures span zero,

one, two, and three dimensions, on the basis of the different binuclear SBUs and

different coordination modes of APD. The Ni-based cluster is a molecular binuclear

nickel cluster. Different dinuclear SBUs are observed in compounds which depend

on the different coordination modes of APD. They also exhibit different photo-

luminescence properties.24 Self-assembly of 4-hydroxypyridine-2,6-dicarboxylic acid

(H3CAM) and pyridine-2,6-dicarboxylic acid (H2PDA) with Zn2+ salts under

hydrothermal conditions yields the coordination polymers {[Zn(HCAM)] �H2O}n

Fig. 4 Molecular structure of the inclusion complex [C6H6 C {Ni(m-StBu)(m-mtet)}10] � 2C6H6.



and {[Zn(PDA)(H2O)1.5]}n. These comprise a 2D (4,4) net and a 1D zigzag chain,

respectively. The reactions of H3CAM and H2PDA with Nd2O3 in the M/L ratio 2:3

gave {[Nd2(HCAM)3(H2O)4] � 2H2O}n and {[Nd2(PDA)3(H2O)3] � 0.5H2O}n. In the

former, a square motif as a building block constructed by four Nd(III) ions was

further assembled into a highly ordered 2D (4,4) grid whereas the latter is a 3D

microporous coordination polymer.25

Two microporous cobalt(II) polymers, [Co(HAIP)2]n � 3nH2O and [Co(AIP)-

(H2O)]n (AIP = 5-aminoisophthalate) have been hydrothermally syn-

thesized and are constructed from the same Co2(CO2)2 secondary building

units, which are extended into a 1D chain in former and a 2D layer in the latter

complex.26

6. Capsules and cages

A novel disk-shaped tris-monodentate ligand L38 has been described which

forms 10 structurally equivalent coordination capsules, [M6(L38)8]12+, with

a series of divalent d5–d10 transition-metal ions, where M = Mn, Fe, Co, Ni, Pd,

Pt, Cu, Zn, Cd, and Hg. The resulting complexes have an octahedral structure

whereby the six metal ions lie on the apices and the eight sides are occupied

with eight ligands. X-ray structural analysis of a single crystal of [Hg6(L38)8-

(CF3SO3)12] revealed a 3-nm-sized octahedron-shaped capsule structure, with sides

of 1.8 nm in length.27

The one-step formation of a 22 component molecular nanospheroid assembly

consisting of six C-pentylpyrogallol[4]arene molecules L39 and 12 Ga3+ metal-ions

which in turn enclose 1150 A3 of space has been reported. This multicomponent

assembly is stabilized by metal-ion coordination and hydrogen bonding interactions.

The nanospheroid array, formed by the reaction of L39 with Ga(NO3)3 consists of

six molecules of C-pentylpyrogallol[4]arene, 12 Ga3+ metal-ions, and 4 water

molecules located within the nanospheroid. The calixarenes are arranged at the

vertexes of a squeezed octahedron which defines the cavity.28



The unprecedented selective encapsulation of trans-[Co(en)2Cl2]+ from the mix-

ture of trans and cis isomers into the cavity of macrocyclic cavitand cucurbit[8]uril

(CB[8]) has been achieved which leads to the inclusion compound {trans-

[Co(en)2Cl2]@CB[8]}Cl, Fig. 5. It was found that the encapsulation within the

CB[8] cavity significantly alters the properties of guest cation trans-[Co(en)2Cl]+ in

both the solid state and solution. Inclusion increases the thermal stability of the

metal complex and blocks its tendency to isomerize into the cis form. Furthermore,

single-crystal X-ray analysis, 1H NMR, and ESI-MS spectra confirm the formation

of the host–guest complex in both solid state and solution, and the geometry of the

complex cation alters significantly upon inclusion, which causes appreciable hypso-

chromic shifts of the absorption bands of the guest complex.29

Red-shifted luminescence from naphthalene-containing ligands due to p-stackingin self-assembled coordination cages has been observed with ligands L40 and L41

after complexation and self assembly into cage structures with Zn2+. In these cages

the presence of extensive aromatic p-stacking between adjacent ligands results in a

redshifted ‘excimer-like’ luminescence which is diagnostic of cage formation.30



The reaction of 4-ethynylpyridine with tert-butyl lithium followed by its addition

to (Me3tacn)RhCl3 (Me3tacn = N,N0,N00-trimethyl-1,4,7-triazacyclononane) affords

the facial octahedral complex (Me3tacn)Rh(CCPy)3, condensation of which with the

square planar complex cis-(DCPE)Pt(NO3)2 results in a self-assembled trigonal

bipyramidal cage with Rh(III) and Pt(II) atoms occupying the vertices (Fig. 6).31

7. Helices

Three isomeric dinuclear unsaturated ruthenium(II) complexes each with a different

double-stranded supramolecular architecture have been synthesized by the reaction

between a dinucleating bisazopyridine ligand with a di(4-phenyl)methane spacer

(L42), which is the azo analogue of the bispyridylimine ligand systems, and

[RuCl2(dmso)4].

The three isomers comprise an arc-shaped nonhelical metallocyclophane (Fig. 7),

an unsaturated conventional double helicate, and a new type of double helicate, in

which just one of the two metal centres is responsible for imparting helicity to the

ligand strands. Moreover, these compounds are the first compounds to bridge the

fields of metallosupramolecular architecture and anticancer drug design. The initial

cell-line experiments showed that the compounds show very good activity. The

isomeric dinuclear [Ru2Cl4L2] complexes reported herein are among the first, and to

date the most promising, dinuclear ruthenium anticancer agents.32

Fig. 5 Top view of the structure of the inclusion complex {trans-[Co(en)2Cl2]@CB[8]}Cl.



Actinide quadruple-stranded helical supramolecular architectures have been

synthesized in which two capped square-antiprismatic ThIV centres are coordinated

by four bisbidentate 4-acylpyrazolone chelating strands. The ThIV quadruple-

stranded helicate complexes were prepared by treatment of ThIV tetrakisacetyl-

acetonate with two equivalents of bisbidentate pyrazolone ligands H2L43 or H2L44

in a solution of MeOH/CHCl3 (1:1). These ThIV complexes are found to have the

M2L4 stoichiometry. Fig. 8 shows the crystal structures of complexes

[Th2(L43)4(dmf)2] and [Th2(L44)4(dmf)2]. These complexes are the first structurally

characterized examples of bisbidentate quadruple-stranded helical complexes and

Fig. 6 Crystal structure of trigonal bipyramidal cage portion of the Rh(III)/Pt(II) complex.



are another remarkable example of cluster formation by incommensurate coordina-

tion number.33

The syntheses and the structures of three (two ruthenium and one rhodium)

hexanuclear complexes, which were obtained by base induced assembly of organo-

metallic half-sandwich complexes [(Z6-C6H5Me)RuCl2]2 and [(Z5-C5Me4H)RhCl2]2,

with bis(dihydroxypyridine) ligands L45–L47 of piperazine, N,N0-dimethylethylene-

diamine, or 1,3-di(4-piperidyl)propane have been reported.34 The complexes display

a unique structural motif: two chiral [(p-ligand)M]3L3 fragments are connected by

three flexible linkers. They can thus be described as expanded triple-stranded

helicates. The synthetic concept appears to be quite flexible because the bridging

ligand as well as the metal fragment can be varied. Complexes of this kind are

expected to display an interesting host–guest chemistry because they contain 12-

Fig. 7 Structure of the metallocyclophane ruthenium complex derived from L42.



metallacrown-3 sites, which should be suited for the complexation of small metal

ions, as well as a flexible cavity decorated by amine groups.34

Two unsymmetrical ditopic hexadentate ligands (L48, L49) designed for the

simultaneous recognition of two different trivalent lanthanide ions have been

synthesized.

Under stoichiometric 2:3 (Ln/L) conditions, these ligands self-assemble with

lanthanide ions to yield triple-stranded bimetallic helicates. The crystal structures

of four helicates with L49 of composition [LnLn0(L49)3](ClO4)6 (CeCe, PrPr, PrLu,

NdLu) show the metal ions embedded into a helical structure with a pitch of about

13.2–13.4 A. The metal ions lie at a distance of 9.1–9.2 A and are nine-coordinated

by the three ligand strands, which are oriented in a head–head–head fashion, where

all ligand strands are oriented in the same direction. In the presence of a pair of

different lanthanide ions in acetonitrile solution, the ligand L49 shows selectivity and

gives high yields of heterobimetallic complexes. L48 displays less selectivity, and this

is shown to be directly related to the tendency of this ligand to form high yields of

head–head–tail isomer. A fine-tuning of the head–head–head—head–head–tail

equilibrium and of the selectivity for heteropairs of LnIII ions is possible.35

Fig. 8 Wire representations of the crystal structure of (a) [Th2(L43)4(dmf)2] and (b)

[Th2(L44)4(dmf)2] as viewed perpendicular to the twofold axis of the quadruple-stranded

helicate. For clarity, each ligand strand is represented in a different colour.



Chiral spontaneous resolution of silver double helicates Ag2L22+ is realized from

achiral ligands, L50 N0,N0-bis[1-(imidazol-4-yl)methylidene]benzil dihydrazone and

L51 N0,N0-bis[1-(pyridin-2-yl)methylidene]benzil dihydrazone.

It was observed that the atropisomer chiral bridging mode of the ligands translates

the chirality of the first metal center to the second one, resulting in the formation of

the chiral helicate, and the intermolecular C–H� � �p and p–p stacking interactions are

expected to be homochiral and strong enough to control the chiral aggregation, from

which conglomerates are formed and spontaneous resolution on crystallization is

achieved.36 A study involving four tritopic polypyridine ligands, L52–L55, in

solutions containing different mixtures of ZnII, CuII and CuI cations has been

undertaken. These represent dynamic combinatorial libraries distributed in accord

with thermodynamic preferences, resulting from the nature of the coordination

environments. By establishing a complex system of constitutionally dynamic metal-

losupramolecular species, in this case double helicates, the possibility of informa-

tion-directed self-assembly by self selection of the correct double strand/metal cation

partners from an equilibrating set of polytopic strands and metal cations could be

observed using electrospray mass spectrometry.37

Reaction of a bent py-hyz-pym-hyz-pym L56 and of a linear py-hyz-py-hyz-pym

L57 (py = pyridine; pym = pyrimidine; hyz=hydrazone) ligand strands with

silver(I) tetrafluoroborate in CH3NO2 generates double-helical dinuclear and tri-

nuclear complexes. These complexes form polymeric, highly ordered solid-state

structures, with wire-like, linear continuous or discontinuous polycationic Agn+

arrays with Ag–Ag distances of 2.78 to 4.42 A. Ligand L58, an isomer of L56, is

found to yield a [2 � 2] grid-type complex. Titration experiments reveal the

formation of linear rack-type dinuclear species. Acid–base modulated, reversible

interconversion between strands and double helicates may be achieved by using tren

as a competing complexing agent (tren = N(CH2CH2NH2)3).

The present results show that the easily accessible hydrazone-connected ligands

L56 and L57 react with Ag(I) ions to produce the double-helical complexes by



coordination of the metal ions to the terminal py-hyz units of the two ligand strands.

These complexes undergo poly association in the solid state to generate self-

assembled highly ordered polymeric architectures containing linear arrays of silver

ions with, depending on the ligand structure, two types of polynuclear Ag+ ionic

sequences; a discontinuous one with ligand L56 and a continuous one with ligand

L57. Such architectures are models for linear wire-like polymetallic nanostructures

and represent building blocks for the design of solid state Ag(I)-based metallo

supramolecular assemblies.38

Two self-assembled meso-helicates of linear trinuclear nickel(II)–radical complexes

with triple pyrazolate bridges are reported whereby complexation of 3-nitronyl-

nitroxide-substituted pyrazolate (pzNNH) L59 and 3-imino-nitroxide-substituted

pyrazolate (pzINH) L60 with nickel(II) gave [Ni3(pzNN)6] and [Ni3(pzIN)6], respec-

tively.

These linear trinuclear complexes were practically isomorphous with neighboring

nickel ions triply bridged by pyrazolate moieties. The space groups were P21/n

but the molecules have a pseudo three-fold axis and the opposite chirality around

the inversion centre at the central nickel(II) ion leads to a meso-helical symmetry in

the whole molecule. See Fig. 9 for the structure of one such complex. The radical

oxygen atoms participate in the 6-membered chelation at the terminal nickel(II)

ions.39

A double helical cobalt complex [(L61)Co2(CH3CN)4][ClO4]4 with two hepta-

dentate Co(II) sites has been isolated from the oligomers formed by the self assembly

of the multidentate ligand 2,3,5,6-tetrakis(2,2 0-bipyridyl)pyrazine (L61) and divalent

cobalt.



The X-ray structure of this complex confirmed the double-helical structure with

two heptadentate Co(II) sites, and a helical pitch of ca. 28.1 A. Coupled Co(I/II)

redox processes are also observed between the two metal centres.40

An enantiomerically pure C2-symmetric salen ligand L62 with benz[a]anthracene

side arms produces M helical complexes with FeII and ZnII in solution which show

varying degrees of attractive p–p stacking for the overlapped benz[a]anthryl side arms.

It is observed that in THF, theM conformer predominates for both the ZnII and FeII

complexes. The ZnII complex maintains this structure in the solid state, but the FeII

complex crystallizes as a 1:1 mixture of diastereomeric helices from pyridine.41

Three helical supramolecular stereoisomers of meso-2, D-2, and D-3 with the

formula of cis-[Ni(f-rac-L)][Ni(CN)4] were successfully constructed based on the

[Ni(f-rac-L63)2+ and [Ni(CN)4]2� building blocks (L63 = 5,5,7,12,12,14-hexa-

methyl-1,4,8,11-tetraazacyclotetradecane).

In all three supramolecular stereoisomers, cis-[Ni(f-rac-L63)]2+ cations are alter-

nately bridged by [Ni(CN)4]2� anions through two cis (in meso-2 and D-2) or trans

(in D-3) cyano groups to form one-dimensional (1D) helical chains of cis-[Ni(f-rac-

L)][Ni(CN)4]. In meso-2, the right/left-handed chirality of the originally formed

chain is transferred oppositely to adjacent chains through the interchain hydrogen-

bonding interactions of hexameric water clusters, leading to the formation of meso-2

with a central symmetrical space group, P21/n, in which the 1D helical chains are

packed in an alternating right- and left-handed chirality. In D-2 and D-3, the right/

left-handed chirality of the original chain is transferred uniformly to adjacent chains

through the zipper-like interchain hydrophobic interactions, resulting in the forma-

tion of D-2 and D-3 with chiral space groups of P212121 and P3121, respectively, in

which all of the 1D helical chains are arranged in the same right/left-handed

chirality. A detailed structural investigation indicates that the interchain hydro-

gen-bonding and hydrophobic interactions play a key role in the transfer of chirality



between neighbouring helical chains, leading to the 1D helical chains being packed in

an achiral or homochiral manner.42

Helical metallo-host–guest complexes via site selective transmetallation of homo-

trinuclear complexes has been achieved using an interesting bis(N2O2) chelate ligand

H4L64 that affords a C-shaped O6 site on the metallation of the N2O2 sites.

UV-Vis and 1H NMR titration showed that the complexation between H4L64 and

zinc(II) acetate affords the 1:3 complex [(L64)Zn3]2+ via a highly cooperative

process. Although the O6 recognition site of the dinuclear metallohost [LZn2] is

filled with an additional Zn2+, the O6 site can bind a guest ion with concomitant

release of the initially bound Zn2+. The novel recognition process ‘‘guest exchange’’

takes place quantitatively when rare earth metals are used as a guest. In the case of

alkaline earth metals, selectivity of Ca2+ 4 Sr2+ 4 Ba2+ c Mg2+ was observed.

However, transmetallation did not take place when alkali metals were used for the

guest. The trinuclear complex [LZn3]2+ is excellent in discriminating charge of the

guest ions. The metallo host–guest complexes thus obtained have a helical structure,

and the radius d and winding angle y of the helix depend on the size of the guest. The

La3+ complex has the smallest y (2881), and the Sc3+ complex has the largest y(3451). Because the radius and winding angles of helices are tunable by changing the

guest ion, the helical metallohost–guest complexes can be seen as a type of molecular

spring or coil. Therefore, the site-specific metal exchange of the trinuclear complex

[LZn3]2+ described here is utilized for selective ion recognition, site-selective

synthesis of (3d)2(4f) trimetallic complexes, and construction of ‘‘tunable’’ metallo-

helicenes.43

Fig. 9 Representation of the structure of the [Ni3(pzIN)6], a meso helicate complex.



A simple and straightforward synthesis of arene ruthenium metallo-prisms is

reported. Self-assembly of 2,4,6-tripyridyl-1,3,5-triazine (tpt) subunits with arene

ruthenium building blocks and oxalato bridges affords cationic triangular metallo-

prisms of the type [Ru6(arene)6(tpt)2(C2O4)3]6+ (arene = C6Me6 and p-PriC6H4Me);

the unexpected double helical chirality of the metalloprisms observed in the solid

state persists in solution giving rise to two different stereodynamic processes as

demonstrated by NMR.44

Four homochiral porous lanthanide phosphonates, [Ln(H2L)3] � 2H2O, (H3L =

(S)-HO3PCH2-NHC4H7-CO2H, Ln = Tb, Dy, Eu, Gd), have been synthesized

under hydrothermal conditions. These compounds are isostructural and they possess

a 3D supramolecular framework built up from 1D triple-strand helical chains. Each

of the helical chains consists of phosphonate groups bridging adjacent Ln(III) ions.

The helical chains are stacked through hydrogen bonds to form 1D tubular channels

along the c axis. Moreover, helical water chains are located in the 1D channels and,

after removal of these water chains, the compounds exhibit selective adsorption

capacities for N2, H2O and CH3OH molecules. Such chiral porous materials hold

promise in applications such as enantioselective separation and heterogeneous

asymmetric catalysis.45

A new route for the synthesis of coordination compounds with dimethyl sulfide

(DMS) ligands has been reported in which the DMS is formed during reaction by the

reduction of dimethyl sulfoxide (DMSO). A luminescent 2-D double-layered polymer,

[(CuI)4(CH3SCH3)3]N, containing helical chains has been constructed by flower-basket-

shaped Cu4I4 clusters. This new cluster is an open cubane-like Cu4I4 cluster and is

further assembled to form a 2-D polymer with unique helical structure. The results are

interesting not only for the preparation of a new luminescent polymeric compound with

CuxIy blocks but also for a new route for synthesis of coordination compounds with

DMS by using DMSO as a starting material instead of the disfavoured DMS.46

8. Networks

Neutral trinuclear (triangular) copper(II) complexes of type [Cu3L3] incorporating the

1,4-aryl linked bis-b-diketonato bridging ligands, 1,1-(1,4-phenylene)-bis(butane-1,3-

dione) (H2L65), 1,1-(1,4-phenylene)-bis(pentane-1,3-dione) (H2L66) and 1,1-(1,4-phe-

nylene)-bis(4,4-dimethylpentane-1,3-dione) (H2L67) have been synthesized.

These complexes were found to act as ‘platform-like’ precursors which on reaction

with selected heterocyclic nitrogen donor bases generate extended supramolecular

architectures. On reaction with 4,40-bipyridine (bipy), [Cu3(L65)3] yields polymeric

structures of type {[Cu3(L65)3(bipy)(THF)]}n and {[Cu3(L65)3(bipy)(THF)] � bipy}nwhile with pyrazine (pyz), {[Cu3(L65)3(pyz)]}n was obtained. Each of these extended

structures contain alternating triangle/linker units in a one-dimensional polymeric



chain arrangement in which two of the three copper sites in each triangular ‘platform’

are formally five-coordinate through binding to a heterocyclic nitrogen atom. Inter-

action of the multifunctional linker unit hexamethylenetetramine (hmt) with

[Cu3(L66)3] afforded an unusual, chiral, three-dimensional molecular framework of

stoichiometry [Cu3(L66)3(hmt)]n. The latter incorporates the trinuclear units coordi-

nated to three triply bridging hmt units. In marked contrast to the formation of the

above structures incorporating bifunctional linker units and five-coordinate metal

centres, the trinuclear platform [Cu3(L65)3] reacts with the stronger difunctional base

1,4-diazabicyclo[2.2.2]octane (dabco) to yield a highly symmetric trigonal columnar

species of type {[Cu3(L67)3(dabco)3] � 3H2O}n in which each copper centre is octahed-

rally coordinated.47 New examples of adducts between di- (and, in one instance, tetra-)

functional nitrogen ligands and planar ‘platform-like’ dinuclear copper(II) complexes,

[Cu2(L68)2], incorporating the 1,3-aryl linked bis-b-diketonato bridging ligand 1,10-

(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione) (H2L68) have also been explored.

The ditopic bridging units employed in the present studies were aminopyrazine

(apyz, L69), 1,4-diazabicylco[2.2.2]octane (dabco, L70), 4,40-dipyridyl sulfide (dps,

L71), dipyridylamine (dpa, L72) as well as bis-pyrazole system, 4,40-(1,3-xylylene)-

bis(3,5-dimethylpyrazole) (xbp, L73). The nature of the product obtained on using

the potentially tetradentate linker hexamethylenetetramine was also elucidated.



The interaction of [Cu2(L68)2] with the ditopic ligand apyz yielded the sandwich-

like tetranuclear species [(Cu2L682(apyz))2]. A variable-temperature magnetochem-

ical investigation of this product indicated weak antiferromagnetic coupling between

the (five-coordinate) copper centres, mediated by the 2-aminopyrazine linkers. An

analogous structure, [(Cu2L682(dabco))2], was generated when dabco was substi-

tuted for aminopyrazine while use of dps and xbp as the ditopic ‘spacer’ ligands

resulted in polymeric species of type [Cu2L682(dps)]n and [Cu2L682(xbp)]n, respec-

tively. These latter species exist as one-dimensional chain structures in which

copper(II) centres on different dinuclear platforms are linked in a ‘zigzag’ fashion.

In contrast, with 2,20-dipyridylamine (dpa) a discrete complex of type [Cu2L682-

(dpa)2] was formed in which one potential pyridyl donor from each 2,20-dipyridyl-

amine ligand remains uncoordinated. The use of the potentially quadruply-bridging

hexamethylenetetramine (hmt, L74) ligand as the linker unit was found to give rise to

an unusual two-dimensional polymeric motif of type [(Cu2(L682)2)3(hmt)2]n. The

product takes the form of a (6,3) network, incorporating triply bridging hexa-

methylenetetramine units.48

The synthesis and characterization of the first examples of organic-soluble

transition-metal phosphates with cores that resemble the double-four-ring secondary

building units (SBU)s of zeolites have been reported. These zinc phosphate cubes are

prepared by reacting Zn(OAc)2 � 2H2O and 2,6-di(isopropyl)phenylphosphoric acid

in methanol in the presence of properly substituted pyridine ligands in the reaction

mixture. The additional functional groups, namely NH2, OH and CH2OH were

placed in appropriate positions on the pyridine ring to enhance hydrogen bonding

between the D4R cubes, thus resulting in noncovalently linked 1D, 2D and 3D

structures. These studies suggest that it is very important to have a hydrogen-bond

donor on the pyridine ligand at an appropriate position. The presence of NH, NH2

or OH groups on the surfaces of these clusters opens up new possibilities for

further reactions with metal alkyl reagents to build dendritic heterometallic super-

structures.49

A new two dimensional compound {[KCuII6(bdap)6(m1,3-SCN)3CuI(NCS)]-

(SCN)4}n, has been prepared and its magnetic properties analysed. The structure

is made up of a potassium cation sandwiched between two triangular tricopper(II)

units, connected to six similar adjacent sandwiches by [(m1,3-SCN)3CuI(NCS)]3�

groups to form an infinite 2D network structure. The positive charge of the

{K[CuII3O3]2[CuI(SCN)4]}

4+ unit is compensated by four free thiocyanate anions.

The system does not behave as a 2D magnet, and the intramolecular magnetic

interactions between the copper(II) ions, mediated by the alkoxo bridge of the bdap

ligand, were found to be antiferromagnetic. One another important aspect about this

structure is that it reveals a new environment of the potassium cation, being in a

tricapped trigonal prism [O6N3].50

The synthesis and characterization of a Pt(II) molecular square with capping

[9]aneS3 ligands, formed via self-assembly mediated by Pt(II) has been reported. The

four corners of this complex are comprised of Pt(II) ions, each one coordinated by

one [9]aneS3 ligand and bridged by four (4,40-bipy) ligands. All four corners of this

complex show the axial Pt–S interactions that account for the unusual Pt(II)

coordination chemistry of [9]aneS3. As expected, each one of the four [9]aneS3ligands is fluxional on the rigid Pt(II) square metal–organic framework, ‘‘turning like

four wheels on a wagon’’.51

Tetrametallic rectangular box complexes are prepared by the reaction of

a heteroligated Rh(I) bimetallic macrocycle with rigid ditopic ligands (1,4-di-



cyanobenzene, 4,40-dicyanobiphenyl, or dipyridyl terminated salen ligand). Forma-

tion of this macrocycle demonstrates the applicability of heteroligated complexes as

novel building blocks where a single coordination site at each Rh centre can be used

to template the assembly of higher ordered multimetallic architectures.52

9. Porphyrins

A new concept of the use of twinning polymers that act as helical hosts to include a

conjugate polymer has been introduced. In order to achieve this, oligomeric

porphyrins are designed such that in their energy minimized state, these oligomers

form helical structures in which a coordinative open face of the Zn porphyrin unit is

always turned inwards so that the central metal ion can interact with the included

conjugated polymer. Based on studies using conjugated polymers bearing coordi-

native amino groups and porphyrin oligomers bearing R groups to control the

spacing between the porphyrin oligomer/conjugated polymer composites and also to

increase the solubility in organic solvent, it is proposed that the porphyrin oligomers

twine around the conjugated polymer strands and the resulting composite aggregate

into relatively large 2D structures in the solid state.53

Monomeric and dimeric iron N-confused porphyrin (NCP) complexes with a bio-

related phenolate as the axial ligand have been synthesized and characterized. The

dimeric NCP complex exhibits a novel NCP architecture with sodium ions bridging

in between the axial phenolate oxygen and peripheral nitrogen on the paired NCP

complexes to give a rectangular type shape. See Fig. 10 for the structure of one such

complex. Importantly, the dimer assembles into a channel-like geometry in the

crystal lattice to form a rare well-organized architecture in the NCP complexes. The

data of the monomeric complex are in agreement with a high spin iron(II) centre. The

dimeric iron(III) complex obtained from the oxidation of the monomer demonstrates

a new method to create a central core within a hydrophobic porphyrinic environ-

ment taking advantage of the peripheral nitrogen and axial ligand.54

A systematic study of axially bound benzoates to aluminium(III) porphyrins and

their potential use as supramolecular building blocks has been presented. The

synthesis of aluminium(III) porphyrin is achieved by the addition of benzoic acid

to a solution of the reactive intermediate generated by the addition of

Fig. 10 A dimeric NCP complex exhibiting a rectangular type NCP architecture.



trimethylaluminium to tetraphenylporphyrin. The axially-bound benzoate ligand is

not displaced by water but exchange does occur with excess competitive carboxylic

acids. The vacant sixth coordination site of the aluminium(III) porphyrin can be

filled by neutral nitrogen donor ligands. The binding of 4-tert-butylpyridine or

N-methylimidazole was confirmed by UV-Vis spectroscopy. Single crystal X-ray

analysis (Fig. 11) confirms the coordination of 4-tert-butylpyridine to the vacant site

of the aluminium(III) porphyrin. These aluminium(III) porphyrins effectively have

two independent faces capable of binding both an oxygen donor and nitrogen donor,

simultaneously, in the axial positions. This robustness and ability to coordinatively

differentiate the two sides of the porphyrin make them an attractive alternative to

tin(IV) porphyrins.55

Reversible switching between intra- to inter-molecular electron transfer pathways

has been accomplished by adding and extracting potassium ions to the supramole-

cular porphyrin–fullerene conjugates made by complexing porphyrin functionalized

with a benzo-18-crown-6 entity and fullerene functionalized with an alkylammonium

cation entity. The intra- to inter-molecular switching was achieved by the addition of

potassium cations which dissociated the crown ether–alkylammonium complex,

while inter- to intra-molecular switching was achieved by the addition of

18-crown-6 to extract the potassium ions of the porphyrin–crown entity.56 The

preparation of supramolecular porphyrin prisms via coordinative self-assembly has

been reported. These prism-shaped assemblies featuring three, six or nine porphyrins

and comprising, respectively, triplicate sets of porphyrin monomers, dimers or

trimers are found to be highly chromophoric and the largest of the prisms resists

break up in the presence of excess linker ligand.57

The photophysical, electrochemical and self-assembly properties of a new triply

fused ZnII–porphyrin trimer were investigated and compared to the properties of a

triply fused porphyrin dimer and the analogous monomer. In the presence of

trifluoroacetic acid, the trimer forms extremely strong and nearly irreversible

Fig. 11 Ball and stick representation of 4-tert-butylpyridine coordinated aluminium porphyrin

complex.



supramolecular interactions with single-walled carbon nanotubes (SWNTs), result-

ing in stable solutions of porphyrin–nanotube complexes in THF. Atomic force

microscopy (AFM) was used to observe the supramolecular porphyrin–nanotube

complexes and revealed that the porphyrin trimer formed a uniform coating on the

SWNTs.58

A supramolecular, three-component AnBmCl bis(zinc porphyrin) tweezer has been

prepared using the heteroleptic bisphenanthroline. Upon addition of spacers of

different length, e.g. 4,40-bipyridine and 1,4-diazabicyclo[2.2.2]octane, to set up an

additional orthogonal binding motif (ZnPor–Nspacer), three structurally different,

four-component AnBmClDk assemblies were formed. The structures of these assem-

blies were named as a bridged monotweezer A2BC2D, a doubly bridged double

tweezer A4B2C4D2, and a triply bridged double tweezer A4B2C4D3, the latter

resembling a porphyrin stack. It was observed that the same structures were equally

formed directly from a mixture of the constituents A, B, C, and D put together in

any sequence if the correct stoichiometry was applied.59 Structural studies of a new

set of zinc porphyrin receptors appended with amide and amide-imidazolium groups

show that the zinc is five coordinate, with pyridine as the fifth coordinating ligand

(see Fig. 12). Anion titration studies reveal the positively charged tetra-imidazolium

zincmetalloporphyrin receptor strongly binds anions in a cooperative 1:1 manner.

Further, the charged receptor is found to be a superior anion binding reagent to the

neutral amide zinc porphyrin, being capable of strong and selective complexation of

sulfate in aqueous–DMSO solvent mixtures.60

A 2-D infinite 22.2 A square-grid coordination network was prepared from a

dicopper(II) tetraacetate [Cu2(AcO)4] as a linear linker motif and 5,10,15,20-tetra-4-

pyridyl-21H,23H-porphine (H2TPyP) as a four-connected vertex, forming a regular

high-porous structure. The characterization by N2 adsorption indicated that this

coordination network has uniform micropores and gas adsorption cavities.61 A

general and high yielding synthetic protocol for the preparation of flexible metal-

directed supramolecular co-facial porphyrin complexes through the use of new

hemilabile porphyrin ligands with bifunctional ether-phosphine or thioether-phos-

phine substituents at the 5 and 15 positions on the porphyrin ring has been reported.

The resulting architectures contain two hemilabile ligand-metal domains (RhI or CuI

Fig. 12 Crystal structure of one pyridine coordinated Zn porphyrin receptor.



sites) and two co-facially aligned porphyrins (ZnII sites), offering orthogonal

functionalities and allowing these multimetallic complexes to exist in two states,

‘‘condensed’’ or ‘‘open’’. The change in cavity size allows these structures to function

as allosteric catalysts for the acyl transfer reaction between X-pyridylcarbinol (where

X = 2, 3, or 4) and 1-acetylimidazole.62 Finally, the synthesis of pentameric

and hexameric macrocyclic porphyrin arrays by complementary coordination of

m-bis(ethynylene)phenylene-linked imidazolylporphyrin has been reported and the

proton NMR spectra of these arrays indicate fast rotation of the porphyrin moieties

along the ethyne axis.63

10. Polyoxometallates

A carefully controlled polymerization reduction process has been reported by which

two predominant structural types of giant polyoxometallates- cyclic, or ring shaped

structures and hollow, spherical structures- are combined together leading to a single

mesoscopic molecule. The synthesis of this novel molecule is achieved by the

acidification of a mixture of vanadate and molybdate followed by controlled

reduction with hydrazine sulfate and subsequent addition of KCl leading to a vana-

dium(IV)-containing nanoring-nanosphere assembly, K43Na11(VO)4[{MoVI72VIV

30-

O282(H2O)66(SO4)12}{MoVI114MoV28O432(OH)14(H2O)58}] ca. 500 H2O {Mo214V30}.

Structural investigation of this giant molecule reveals an open ‘‘clam-like’’ nano-

scopic assembly (ca. 6 nm in length) comprising a spherical {MoVI72VIV

30} anion

and a ring-shaped {Mo142} anion linked by two K centres acting as a hinge.

Interestingly, the spherical subunit present in this molecule exhibits a regular

icosahedral structure (virtual Ih symmetry) in contrast to the previously reported

more distorted D5d {Mo72V30} cluster, with potential implications for the magnetic

properties.64

A luminescent logic gate with dual output based on surfactant encapsulated

polyoxometallate complexes (SEC) has been realized by utilizing synergetic inter-

action between each component and taking advantage of the supramolecular self

assembly. The two components of the present SEC, the luminescent polyoxometallo-

europate (Na9EuW10O36) and a multifunctional surfactant trans-10-(4-(40-pyridyl-

vinylene)phenyl)oxydecyldodecyldimethylammonium bromide (PyC10C12N), are

connected together through electrostatic interactions. The dual output logic function

(INHIBIT and NOR) of the reported organic/inorganic hybrid material consisting

of SEC is realized by the supramolecular synergy between the two components.

Also, the present methodology indicates that, besides organic molecules, the

inorganic nanosized materials can be introduced into the logic gate as well.65

A range of complexes based on the high-nuclearity {W36} isopolyoxotungstate

cluster, [H12W36O120]12–, with a triangular topology have been isolated by using the

organic cation, protonated triethanolamine. It was found that the cluster can form

alkali and alkaline earth metal complexes {MCW36} (M=K+, Rb+, Cs+, NH4+,

Sr2+ and Ba2+) analogous to 18-crown-6 crown ether. These complexes demon-

strate that the {W36} can act like a kind of inorganic ‘‘crown ether’’ with similar

preferences to 18-crown-6, but with much greater rigidity and, therefore, potential to

distinguish between different cations.66

A detailed investigation of the voltammetric, photophysical and photo-electro-

chemical properties of the Dawson polyoxometalate anions a-[S2M18O62][4–] (M =

Mo, W), in the absence and presence of a series of [RuIILn]+/2+ cations [Ln =

(bpy)3, (bpy)2(Im)2, (bpy)2(dpq), (bpy)2(box) and (biq)2(box)] has been presented.



A series of salts [RuLn]2[S2M18O62] were isolated in substance and their voltammetry

studied in both the solution and solid states; reversible reduction of anions were

observed at similar potentials in the presence or absence of cations [RuLn]2+.

Photolysis experiments were performed on solutions of the salts [R4N]4[S2M18O62]

(R = n-butyl or n-hexyl) and [RuIILn]2[S2M18O62] at 355 and 420 nm in dimethyl-

formamide and acetonitrile in the presence and absence of benzyl alcohol (10% v/v).

When associated with [Ru(bpy)3]2+, the molybdate anion exhibited a large increase

in the quantum yield for photo-reduction at 420 nm. The quantum yield for the

tungstate analogue was lower but the experiments again provided clear evidence for

sensitization of the photo-reduction reaction in the visible spectral region. The origin

of this sensitization is ascribed to the new optical transition observed around 480 nm

in static ion clusters {[Ru(bpy)3][S2M18O62]}2– and {[Ru(bpy)3]2[S2M18O62]} present

in solution. Measurable photocurrents resulted from irradiation of solutions of the

anions with white light in the presence of the electron donor dimethylformamide.

Evidence is also presented for possible quencher–fluorophore interactions in the

presence of certain [RuIILn]+ cations.67

11. Miscellaneous

An efficient method for stabilizing highly labile coordinatively unsaturated transi-

tion metal complexes has been reported by Fujita et al. In this work, the direct

crystallographic observation of in situ generated Cp0Mn(CO)2 (Cp0 = methylcyclo-

pentadienyl) by photodissociation of Cp0Mn(CO)3 in a self assembled coordination

cage has been achieved. This represents the much awaited crystallographic evidence

for the geometry of an unsaturated transition metal centre and showed that the 16

electron unsaturated Mn complex adopts a pyramidal geometry. Further, the

structure determination of such a short lived highly reactive species is made possible

mainly due to the highly crystalline nature and high binding ability of the cage used

to entrap the species.68

Self-assembly of hydrogen-bonded aggregates of pyrogallol[4]arene hexamers and

their metal (Ga) coordinated capsules into spherical and tubular superstructures on

the sub-micron scale has been reported. By using various electron or force micro-

scopy techniques these superstructures are shown to link and/or bud from one

another. The tecton here is a near spheroidal hexameric nanocapsule based on

pyrogallol[4]arene, held together by 72 hydrogen bonds, and has lipophilic alkyl

chains of varying length that radiate from the spheroid shell to different extents

depending on the precursor selected. For particular carbon-chain lengths, the

hydrogen-bonded ‘‘seams’’ or ‘‘faces’’ of the spheroid can become exposed (in the

solid state at least) and it is proposed that these combined factors may play a crucial

role in superstructure stabilization on the submicron level. These supramolecular

systems are unique in that the self-assembly of the hexamer takes place prior to the

formation of larger aggregates. Solvent properties are very important in the

formation of these large structures, and an abundance of water appears to hinder

aggregate formation, thereby suggesting that hexamer-to-hexamer interactions may

be disturbed under such conditions. Although the specific inter-hexamer interactions

are unknown to date, the aggregation phenomenon is general for a number of

pyrogallol[4]arenes. The large aggregates may either be stabilized by a large number

of van der Waals interactions between neighbouring alkyl chains, or by face-to-face

hexamer interactions between hydrophilic regions of the discrete supramolecular

assemblies, as is observed in the solid state. The ability to attach a range of



functionalities to the alkyl chains of the nanospheroids, coupled with the ability to

modify the interior of the hexamers with a range of guest molecules will undoubtedly

prove useful in the future study and application of these spherical and tubular sub-

micron assemblies.69

Template directed one step synthesis of cyclic trimers by acyclic diene metathesis

(ADMET) has been achieved. A cyclic trimer L77, based on a DB24C8 acyclic diene

L75, was produced by ADMET at low concentrations in the presence of the

trifurcated template L76-H33+ containing three RCH2NH2

+CH2R recognition

sites. The threading of the monomers onto the template is demonstrated to be vital

for cyclic trimer formation. The reaction scheme involves (I) the complex formation

in a 3:1 molar ratio of the DB24C8 derivative L75 bearing two olefinic sidearms and

the trifurcated trisammonium template L76-H33+ (as its 3BArF� salt) and (II) the

formation of the macrocyclic tris-DB24C8 derivative L77 in one pot as a result of

triple ADMET reactions, catalyzed by ruthenium-alkylidene complexes at relatively

low concentrations.70



A tridentate p-conjugated C,N,Npyrazolyl cyclometallating ligand, 2-phenyl-6-(1H-

pyrazol-3-yl)pyridine (HL78), that contains a Cphenyl, a Npyridyl, and a Npyrazolyl

donor moiety as well as a 1-pyrazolyl-NH that can still be available for further

chemical interactions, such as protonation/deprotonation, after cyclometallation has

been designed. Reaction of HL78 with K2PtCl4 affords the cycloplatinated complex

[Pt(L78)Cl] which further reacts with bis(diphenylphosphino)methane (dppm) to

give the binuclear {[Pt(L78)]2(m-dppm)}(ClO4)2. This complex represents a molecu-

lar ‘‘pivot hinge’’ where the two [Pt(L78)] moieties are held by the diphenylphos-

phino functionalities of the m-dppm with the bridging methylene as the pivot.

Opening and closing of the pivot-hinge is regulated by the deprotonation/protona-

tion of the 1-pyrazolyl-NH of the C,N,N-pyrazolyl ligands.71

Syntheses, spectroscopic and some structural properties of a series of complexes

[Ru(CN)4(HAT)]2�, [{Ru(CN)4}2(m2-HAT)]4� and [{Ru(CN)4}3(m3-HAT)]6� , in

which one, two or three {Ru(CN)4}2� units are connected to the bidentate sites of

the tri-topic ligand hexaaza-triphenylene (HAT) have been reported. These new

polynuclear cyanoruthenate chromophores are of interest for both their structural

properties (in cyanide-bridged coordination networks with high connectivities), and

for their photophysical properties (with the ability to act as panchromatic light

absorbers and energy donors whose properties can be tuned by the nature of the

solvent). The extended aromatic bridging ligand and the presence of up to three

chromophoric centres results in a remarkably intense, low energy, highly solvato-

chromic absorption of light. The complexes [Ru(CN)4(HAT)]2�, [{Ru(CN)4}2-

(m2-HAT)]4� and [{Ru(CN)4}3(m3-HAT)]6� contain four, eight and twelve exter-

nally-directed cyanide ligands, respectively; they show strongly solvatochromic and

intense MLCT absorptions, and [{Ru(CN)4}3(m3-HAT)]6� forms a high-dimension-

ality cyanide-bridged coordination network with Nd(III), in which Ru - Nd energy

transfer results in sensitised near-IR luminescence. The crystal structure of the

Nd(III) salt of Nd2[{Ru(CN)4}3(m3-HAT)] � 23H2O, illustrates the potential of these

high connectivity complex anions as components of coordination networks. The

structure consists of two dimensional sheets (Fig. 13).72

The synthesis of the cage [Eu2Zn4L4(OAc)6(NO3)2(OH)2] � 2Et2O (HL =

5-bromo-3-methoxysalicylaldehyde) has been reported. Molecules of this complex

have an unusual central cage-like cavity, and, in the solid state a combination of

short intermolecular Br� � �O interactions and p–p stacking give rise to a 3-dimen-

sional framework which contains open channels. Guest molecules of diethyl ether or

methanol are reversibly encapsulated in cavities formed by the 3-dimensional

supramolecular framework of heteropolynuclear, luminescent [Eu2Zn4L4(OAc)6-

(NO3)2(OH)2] � 2Et2O.73

Solid state preparation of hybrid organometallic-organic macrocyclic adducts

with long chain dicarboxylic acids has been achieved. The supramolecular



macrocyclic adducts of general formula {[Fe(Z5-C5H4-C5H4N)2] [HOOC(CH2)n-

COOH]}2 with n = 4, 6, 7, 8 have been obtained quantitatively by kneading

powdered samples of the crystalline organometallic and organic reactants with

drops of MeOH. More specifically, manual grinding of the solid organometallic

complex [Fe(Z5-C5H4–C5H4N)2] with the solid dicarboxylic acids of formula

HOOC(CH2)nCOOH [where n = 4 (adipic), 5 (pimelic), 6 (suberic), 7 (azelaic)

and 8 (sebacic)] in the presence of traces of MeOH (by kneading) yields macrocyclic

compounds (for n = 4, 6 and 7) and by direct crystallization from MeOH for n = 8,

while the adduct with n = 5 represents an isomeric open chain alternative to the

macrocycle. In all cases, the organic and organometallic moieties are held together

by hydrogen bonds between the carboxylic –OH groups and the pyridine nitrogen

atoms. Reactions between crystalline solids of the type used to prepare these

macrocycles can be regarded as supramolecular reactions between solid, periodic

supermolecules. In reactions between molecular solid reactants to form a new

molecular solid product, the covalent bonding is not affected, while non-covalent

van der Waals or hydrogen bonding interactions are broken and formed.74 The

coordinative properties of a calix[6]arene presenting nitrogenous binding sites at

each rim has been investigated. The coordination of a first Zn(II) ion to the

calix[6]arene presenting three imidazolyl arms at the small rim and three aniline

moieties at the large rim allows the binding of a second Zn(II) ion while hosting a

(H3O2)� unit in the aromatic cavity.75 Entrapment of a dirhodium tetracarboxylate

unit inside the aromatic bowl of a calix[4]arene has been achieved (see Fig. 14 for the

crystal structure of one such example) and this inclusion complex has been evaluated

for rhodium-catalyzed oxidative amination of saturated C–H bonds. These mixed-

carboxylate systems display estimable performance when compared to other known

Rh dimers.76

Fig. 13 View of the structure of Nd2[{Ru(CN)4}3(m3-HAT)] � 23H2O showing one of the two

dimensional layers present in the molecular structure.



Ag(I) and Cu(I) double-stranded boxes, and Fe(II) and Ni(II) triple-helicates are

synthesized from the isoquinoline-imine ligand L79 and the aggregation of these

imine-based metallo-supramolecular architectures through p–p interactions ex-

plored.

The isoquinoline affords an extended p surface and the use of this surface to

obtain self-recognition and consequent p–p aggregation is investigated. The ap-

proach is effective in that each of the four complexes is observed to aggregate

through these interactions.77

Fig. 14 Crystal structure of a calix[4]arene-derived tetracarboxylate dirhodium(II) inclusion

complex.



The metallosupramolecular tetrahedra M8[L4Ti4] are easily obtained by self-

assembly from the triangular ligands L-H6 and titanoyl bis(acetylacetonate) in the

presence of alkali metal carbonates as base. Force field calculations reveal that the

tetrahedra show Ti–Ti separations of 17 ([L804Ti4]8–) and 23.5 A ([L814Ti4]

8–)

respectively, leading to huge internal cavities. The cavity is readily shielded in the

case of L80 but possesses big pores with the bigger ligand L81. [L804Ti4]8� was used

to investigate the host–guest chemistry of these container molecules and it was found

that cationic organic guest species like anilinium can be introduced in to the interior

of the complex. Inclusion of guests can be followed by NMR spectroscopy and upon

addition of one equivalent of guest the symmetry of the tetrahedron is lost but is

regained after addition of significantly more than four equivalents.78

An interesting dynamic equilibrium has been observed in CDCl3 between a neutral

molecular square, [cis-Mo2(DAniF)2]4(O2CC6F4CO2)4 and triangle, [cis-Mo2(DA-

niF)2]3(O2CC6F4CO2)3 (DAniF = the anion of N,N0-di-p-anisylformamidine). Both

compounds have been characterized crystallographically making this one of the few

examples in which both species in a dynamic equilibrium could be isolated and

analyzed structurally (Fig. 15). The conversion of three moles of molecular squares

to four moles of molecular triangles has an equilibrium constant of 1.98(7) � 10�4 at

23.7 1C. At this temperature, the DG0 for the conversion of three moles of squares to

four moles of triangles is 21.0 kJ mol�1 and the conversion is enthalpically

disfavoured (DH0 = 23.5 kJ mol�1), but entropically favoured (DS0 = 8.2 J K�1

mol�1).79

A cagelike lanthanide cluster {[LaIII18(D-bpba)18(H2O)36]Cl18 � nH2O with a sphe-

rical structure has been synthesized and characterized by X-ray crystallography.

(D-bpba = N,N0-bis(2-pyridylmethyl)-N,N0-1,2-ethanediylbis(D-alaninate)). This

complex is large and the maximum diameter of the overall molecule is ca. 3.2 nm,

and that of the LaIII18 cluster core is ca. 1.9 nm.80 It has been observed that the

binding of 3,5-di-tert-butyl-1,2-benzocatechol (H2DTBC) at ZnII complexes of a

tetradentate, tripodal ligand is significantly enhanced (36–4.6 � 104 fold), and its

reduction potential shifted (90-270 mV) to more positive values by introducing one

to three amino hydrogen bond donors into the host complex. The structure of one of

the complexes is reported and shows intramolecular N–H� � �O hydrogen bonding

between the ligand-based amino group and the ZnII-bound catecholate, which

provides an explanation for the observed behaviour. These begin to show the extent

Fig. 15 Core structures of the molecular square, [cis-Mo2(DAniF)2]4(O2CC6F4CO2)4 and

triangle, [cis-Mo2(DAniF)2]3(O2CC6F4CO2)3.



to which N–H hydrogen bond donors can affect redox potentials and binding of

electroactive substrates bound to a metal centre.81

Recognition of thiolato- and alkoxy-bridged ReI molecular rectangles towards

highly conjugated aromatic guests like pyrene via perfect C–H� � �p interactions was

observed and confirmed by solid state data. This molecular recognition through

weak CH� � �p interactions is a rare example of an interaction that is rarely designed

into a host guest pair.82 Gondola-shaped luminescent tetrarhenium metallacycles

with crown-ether-like multiple recognition sites have been synthesized employing a

new orthogonal-bonding approach for assembling functional molecules. This meth-

od involves the simultaneous introduction of a bis-(chelating) dianion to coordinate

to two equatorial sites of two fac-(CO)3Re cores and a ditopic nitrogen-donor ligand

to the remaining orthogonal axial site, leading to the generation of a new class of

metallacycles. These highly luminescent metallacycles contain crown-ether-like

recognition sites, which are capable of selectively recognizing metal ions and planar

aromatic molecules.83

Four new symmetric and asymmetric oxadiazole-bridging ligands (L82–L85) with

single and double 4- or 3-pyridinecarboxylate arms bridged by a 1,3,4-oxadiazole

ring have been synthesized. L82, L83 and L84 act as convergent ligands and bind

metal ions into discrete molecular complexes while L85 exhibits a divergent spacer to

link metal ions into one dimensional coordination polymers. Further, it was

observed that the different donor orientation of the ligands and the power of anion

templation are the key factors in determining the final structure of the supramole-

cular species formed.84

,

A cavity-containing metal–ligand assembly is employed as a catalytic host for the

3-aza Cope rearrangement of allyl enammonium cations. Upon binding, the rates of



rearrangement are accelerated for all substrates studied, up to 850-fold. Activation

parameters were measured for three enammonium cations in order to understand the

origins of acceleration. Those parameters reveal that the supramolecular structure is

able to reduce both the entropic and enthalpic barriers for rearrangement and is

highly sensitive to small structural changes of the substrate. The space-restrictive

cavity preferentially binds closely packed, preorganized substrate conformations,

which resemble the conformations of the transition states. This hypothesis is also

supported by quantitative NOE studies of two encapsulated substrates, which place

the two reacting carbon atoms in close proximity. Therefore the capsule can act as a

true catalyst, since release and hydrolysis facilitate catalytic turnover. It was

concluded that the iminium product must dissociate from the cavity interior and

the assembly exterior before hydroxide-mediated hydrolysis, and propose the

intermediacy of a tight ion pair of the polyanionic host with the exiting product.85

Transformation of inorganic sulfur to organic sulfur has been observed in the

solvothermal reaction of CuSCN with 1,2-bis(diphenylphosphino)ethane (dppe)

yielding a coordination polymer, which was characterized to be a complex of CuCN

and 1,2-bis(diphenylthiophosphinyl)ethane (dppeS2): [(CuCN)2(dppeS2)]n. The iden-

tification of complex [(CuCN)2(dppeS2)]n revealed that CuSCN was decomposed

and the sulfur was transferred to dppe. Substituting the dppeS2 ligand from the

above complex with strong coordinating ligands 2,4,6-tris(2-pyridyl)-1,3,5-triazine

(tpt), three more new CuCN coordination polymers were synthesized and character-

ized. During the syntheses of these tpt substituted complexes, single crystals of

dppeS2 were isolated, which indicate that it was substituted by tpt ligand and also

confirmed the transformation of sulfur from CuSCN to dppe. The decomposition

reactions of CuSCN seem to be temperature- and solvent-dependent.86

A family of new homochiral 1D coordination polymers based on 46-membered

metallomacrocycles with the enantiopure elongated and bent bipyridine ligand

(S)-2,20-diethoxy-1,10-binaphthyl-6,60-bis(4-vinylpyridine), L86 have been reported.

The framework structures of all these six compounds were found to be built up

from similar 1D polymeric chains composed of 46-membered metallomacrocycles

and mainly four distinct packing patterns were observed. It was found that with the

exception of one case, the anions do not coordinate to the metal centres and reside in

the open channels. The framework structures were found to be tolerant of the change

of metal centres and their local coordination environments.87 The coordination



chemistry of a series of di- and tri- nucleating ligands (L87–L93) which contain two or

three N,N0-bidentate chelating pyrazolyl-pyridine units pendent from a central aro-

matic spacer with Ag(I), Hg(I) and Hg(II) has been investigated. Thirteen complexes of

varying structural types are reported, which include 1D coordination polymers, 2D

coordination network and mesocate or helicate dinuclear complexes from Ag(I). Tree

dinuclear Hg(I) complexes were isolated which contain an {Hg2}2+ metal-metal

bonded core bound to a single bis-bidentate ligand which can span both metal ions.

Also characterised were a series of Hg(II) complexes comprising a simple mononuclear

four-coordinate Hg(II) complex, a tetrahedral HgII4 cage which incorporates a counter-

ion in its central cavity, a trinuclear double helicate, and a trinuclear catenated

structure in which two long ligands have spontaneously formed interlocked metallo-

macrocyclic rings as a result of cyclometallation of two of the Hg(II) centres.88



New Ag(I) supramolecular complexes which exhibit rare C-H� � �Ag hydrogen

bonding interactions have been synthesized by reactions of Ag(I) salts with two well-

designed rigid bulky acridine-based ligands L94 and L95. This work offers three new

rare examples in which the N donors of the acridine rings coordinate to Ag(I) ions in

coordination supramolecular systems. The total interaction energy related to the

hydrogen bonds between H and Ag(I) in one of the complexes is evaluated to be

about 14 kJ mol�1 for the H� � �Ag weak interaction, which is very close to those

values estimated for C–H� � �O and C–H� � �N hydrogen bonds. In addition, NBO and

MO analyses also confirm the presence of C–H� � �Ag weak interaction in this

complex. These results strongly support the existence of the C–H� � �Ag hydrogen-

bonding interactions in the coordination supramolecular systems, which may offer

an effective means for constructing unique supramolecular architectures via

C–H� � �M close interactions.89

3D 3d–4f interpenetrating coordination polymers {[LnCr(IDA)2(C2O4)]}n (Ln =

Eu, Sm) have been discovered by the hydrothermal reaction of Cr(NO3)3, Ln2O3,

and iminodiacetate acid (H2IDA). It was observed that in these reactions, the

H2IDA ligands partly decompose into oxalate anions (ox), which connect LnIII ions

to form 1D {Ln(ox)}n chains. Each of the CrIII ions is tridentate—coordinated by

two IDA ligands, which act as tetradentate metalloligands to link {Ln(ox)}n chains

to form 3D open networks. The interpenetration of two open networks results in

nonporous products.90 Also, 3D layer-pillared homoligand coordination polymers



with 1D and 2D channels are constructed from a 2D layered precursor. Here, a lay-

ered metal-organic framework Zn3(BDC)3(H2O)2 � 4DMF (BDC = terephthalate,

DMF = N,N-dimethylformamide) was fabricated from H2BDC by liquid–liquid

diffusion. This layered metal organic framework was then used as a precursor to

solvothermally react with further H2BDC at 140–180 1C, resulting in two products

of BDC insertion into the layered structure. These are [Zn3(p-BDC)4] � 2HPIP,

(HPIP = partially protonated piperazine), and [Zn3(p-BDC)3(H2BDC)]

(C6H15NO) �H2O � 3DMF, (C6H15NO = triethylamine N-oxide). Crystallography

revealed that these products possess 1D and 2D channels, respectively.91

Microporous NiII coordination polymers with general formula {[Ni2(NCX)4-

(azpy)4] �G}n (X = S/Se, G (guest molecule) = MeOH/EtOH/H2O/no guest) are

prepared with a 4,40-azobis(pyridine) (azpy) ligand. These compounds have one-

dimensional periodic ultramicropores that contain the small guest molecules H2O,

MeOH, or EtOH, the hydroxy groups of which interact with the S or Se atoms of

isothiocyanate or isoselenocyanate, respectively, via –S(Se)� � �HO– hydrogen bonds.

X-ray characterization of the solvated and desolvated structures of the compounds

were almost the same indicating that the ultramicropores are stable without any guest

molecules. The adsorption and desorption experiments indicate that these compounds

have dynamic 1D ultramicroporous channels constructed by an interpenetration that

is not a chemical bonding network but merely a mechanical entanglement.92

Five different multidimensional coordination polymers based on W/Cu/S clusters

with flexible imidazole ligands have been synthesized and structurally characterized.

Depending on the reaction temperature and the reagents used, reactions of [WES3]2�

(E = S, O) with CuX (X = NCS, CN, I) in the presence of bix (bix =

1,4-bis(imidazole-1-ylmethyl)benzene) in DMF or CH3CN resulted in the formation

of two novel 2D - 3D interpenetrating coordination polymers [S2W2S6Cu4(bix)2]nand {[WS4Cu4(NCS)2(bix)3] �CH3CN}n, a noninterpenetrating 3D polymer

{[WS4Cu2(bix)] �DMF}n, and two 2D sheet polymers [WS4Cu3(CN)(bix)]n and

{[OWS3Cu3(bix)2][I] �DMF � 2H2O}n. The first two compounds of this series

[S2W2S6Cu4(bix)2]n and {[WS4Cu4(NCS)2(bix)3] �CH3CN}n represent the first exam-

ples of interpenetrating (4,4) frameworks with clusters and nodes and bidentate

pyridyl-based ligands as linkers.93

A new Janus scorpionate ligand [HB(mtda)3�], which is a hybrid of tris(pyrazo-

lyl)borate and a tris(mercaptoimidazolyl)borate containing mercaptothiadiazolyl

(mtda) heterocyclic rings with both hard nitrogen donors and soft sulfur donors

has been prepared. The differential hard/soft character of the dissimilar donor

groups in this bridging ligand was exploited for the controlled solid-state organiza-

tion of homometallic and heterometallic alkali metal coordination polymers.

Sodium gave coordination polymers with both acentric (with NaS3N3H kernels)

and centric (with alternating NaN6 and NaS6H2 kernels) chains in the same crystal

(where the centricity is defined by the relative orientations of the B–H bonds of the

ligands along the lattice). It was found that for the homometallic potassium

congener, the larger cation size compared to sodium, induced significant distortions

and favoured a polar arrangement of ligands in the resulting coordination polymer

chain. An examination of the solid-state structure of the mixed alkali metal salt

system revealed that synergistic binding of smaller sodium cations to the nitrogen

portion and of the larger potassium cations to the sulfur portion of the ligand

minimizes the ligand distortions relative to the homometallic coordination polymer

counterparts, a design feature of the ligand that is likely to assist in thermodyna-

mically driving the self-assembly of the heterometallic chains.94



An unprecedented crystal growth system of a coordination framework, where the

crystallization occurs through the breaking and forming of covalent bonds has been

reported as a novel approach to control crystal growth rate, direction, and their

time-dependent changes. The coordination framework studied {[Cu3(CN)3{hat-

(CN)3(OEt)3}]}n (hat-(CN)3(OEt)3 = 2,6,10-tricyano-3,7,11-triethoxy-1,4,5,8,9,12-

hexaazatriphenylene) is crystallized through the reaction of 2,3,6,7,10,11-hexacyano-

1,4,5,8,9,12-hexaazatriphenylene (hat-(CN)6), ethanol, and a copper(I) complex,

involving the breaking and forming of covalent bonds. The crystal morphologies

obtained from this system contain dumbbells, cogwheels, and superlattices.95

Solvothermal reactions of Cu(NO3)2 with 3,5-dimethylpyrazole (HPz) and

3,30,5,50-tetramethyl-4,40-bipyrazole (H2Bpz) in presence of NH3 resulted in two

luminescent coordination compounds, [Cu(Pz)]3 and [Cu2(Bpz)]n, respectively of

which the former was revealed to be a planar trimer and the latter a three-

dimensional framework, presenting a rare 3-connected binodal (62.10)(6.102) topo-

logy and eight-fold interpenetration.96

Reversible structural transformation of a non porous 2D spin cross over co-

ordination polymer, {Fe(3-CNpy)2(CH3OH)2/3[Au(CN)2]2} (3-CNpy = 3-CNpyr-

idine), into a triple interpenetrated 3D microporous spin crossover framework with

the NbO structure type, {Fe(3-CNpy)2[Au(CN)2]2} is reported. This system is an

example of crystalline-state ligand exchange reaction involving substitution-active

iron(II) coordination sites able to selectively recognize guest CH3OH molecules.

Reversibility of this crystal-to-crystal transformation is evidenced by X-ray crystallo-

graphic data and from their spin crossover properties.97 A series of pillared helical-

layer coordination polymers are reported by the self assembly of a long V-shaped

3,30,4,40-benzophenonetetracarboxylate ligand and salts of Cu, Mn, Ni, Co, Cd, Mg

and Fe in the presence of linear bidentate ligand 4,40-bipyridine. These complexes

are believed to be the first examples of pillared helical layer coordination polymers.

The V-shaped bptc ligand and V-shaped phthalic group of the bptc ligand are

supposed to be important for the formation of the helical structures.98

A microporous magnetic 3D cobalt(II) coordination polymer [Co2(ma)(ina)]n � 2n-H2O (ma=malate, ina = isonicotinate) featuring pillared layers with a void volume

of 25.8%, was generated by hydrothermal treatment. In this material, the in situ

generated ma ligands connect the CoII ions into a 2D lattice with mixed and multiple

exchange-bridges, affording a new geometrical topology different from the Kagome

lattice and leading to spin frustration. It was found that the rigid ina-pillared

metallic-layered structure retains the 3D structural ordering upon guest removal and

exchange. Single crystals of dehydrated [Co2(ma)(ina)]n were transformed into single

crystals of [Co2(ma)(ina)]n �MeOH and [Co2(ma)(ina)]n �HCONH2 by soaking the

guest-free host in MeOH and methanamide (HCONH2) solutions, respectively

without apparent host-structural changes. [Co2(ma)(ina)]n can also be rehydrated

into [Co2(ma)(ina)]n � 2H2O0. These single-crystal-to-single-crystal transformations

are confirmed by single crystal XRD. The magnetic behaviours of this family of

porous magnetic materials were complex due to the influences of multiple metal sites,

intra- and inter-layer exchanges, spin–orbit coupling, as well as geometrical frustra-

tion.99

References

1 S.-H. Hwang, C. N. Moorefield, P. Wang, F. R. Fronczek, B. H. Courtney and G. R.Newkome, Dalton Trans., 2006, 3518.

2 N. L. S. Yue, M. C. Jennings and R. J. Puddephatt, Dalton Trans., 2006, 3886.



3 D. L. Reger, R. P. Watson and M. D. Smith, Inorg. Chem., 2006, 45, 10077.4 C. D. Pentecost, A. J. Peters, K. S. Chichak, G. W. V. Cave, S. J. Cantrill and J. F.

Stoddart, Angew. Chem., Int. Ed., 2006, 45, 4099.5 H. Bakirci, A. L. Koner, Mi. H. Dickman, U. Kortz and W. M. Nau, Angew. Chem., Int.

Ed., 2006, 45, 7400.6 N. Shan, J. D. Ingram, T. L. Easun, S. J. Vickers, H. Adams, M. D. Ward and J. A.

Thomas, Dalton Trans., 2006, 2900.7 H. Jiang and W. Lin, J. Am. Chem. Soc., 2006, 128, 11286.8 S. K. Dey, L. K. Thompson and L. N. Dawe, Chem. Commun., 2006, 4967.9 J. Ramirez, A.-M. Stadler, N. Kyritsakas and J.-M. Lehn, Chem. Commun., 2007, 237.10 O. Waldmann, M. Ruben, U. Ziener, P. Muller and J.-M. Lehn, Inorg. Chem., 2006, 45,

6535.11 A.-M. Stadler, N. Kyritsakas, R. Graff and J.-M. Lehn, Chem.-Eur. J., 2006, 12, 4503.12 L. J. Childs, J. Malina, B. E. Rolfsnes, M. Pascu, M. J. Prieto, M. J. Broome, P. M.

Rodger, E. Sletten, V. Moreno, A. Rodger and M. J. Hannon, Chem.-Eur. J., 2006, 12,4919.

13 C. B. Aakeroy, N. Schultheiss and J. Desper, Dalton Trans., 2006, 1627.14 A. J. Gallant, J. H. Chong and M. J. MacLachlan, Inorg. Chem., 2006, 45, 5248.15 Y. Sun, K. Ye, H. Zhang, J. Zhang, L. Zhao, B. Li, G. Yang, B. Yang, Y. Wang, S.-W. Lai

and C.-M. Che, Angew. Chem., Int. Ed., 2006, 45, 5610.16 C.-C. You, C. Hippius, M. Grune and F. Wurthner, Chem.-Eur. J., 2006, 12, 7510.17 R. Sekiya, S. i. Nishikiori and K. Ogura, Inorg. Chem., 2006, 45, 9233.18 S. L. Zheng, M. Gembicky, M. Messerschmidt, P. M. Dominiak and P. Coppens, Inorg.

Chem., 2006, 45, 9281.19 X. Lin, A. J. Blake, C. Wilson, X. Z. Sun, N. R. Champness, M. W. George, P.

Hubberstey, R. Mokaya and M. Schroder, J. Am. Chem. Soc., 2006, 128, 10745.20 S. R. Halper, L. Do, J. R. Stork and S. M. Cohen, J. Am. Chem. Soc., 2006, 128, 15255.21 Z. Y. Du, H. B. Xu and J. G. Mao, Inorg. Chem., 2006, 45, 9780.22 C. Zhang, S. Takada, M. Kolzer, T. Matsumoto and K. Tatsumi, Angew. Chem., Int. Ed.,

2006, 45, 3768.23 Q.-R. Fang, G.-S. Zhu, Z. Jin, M. Xue, X. Wei, D. -Jun Wang and S.- L. Qiu, Angew.

Chem., Int. Ed., 2006, 45, 6126.24 Y. Gong, W. Tang, W. Hou, Z. Zha and C. Hu, Inorg. Chem., 2006, 45, 4987.25 H. L. Gao, L. Yi, B. Zhao, X. Q. Zhao, P. Cheng, D. Z. Liao and S. P. Yan, Inorg. Chem.,

2006, 45, 5980.26 E. Tang, Y. M. Dai, J. Zhang, Z. J. Li, Y. G. Yao, J. Zhang and X. D. Huang, Inorg.

Chem., 2006, 45, 6276.27 S. Hiraoka, K. Harano, M. Shiro, Y. Ozawa, N. Yasuda, K. Toriumi and M. Shionoya,

Angew. Chem., Int. Ed., 2006, 45, 6488.28 R. M. McKinlay, P. K. Thallapally and J. L. Atwood, Chem. Commun., 2006, 2956.29 T. V. Mitkina, M. N. Sokolov, D. Y. Naumov, N. V. Kuratieva, O. A. Gerasko and V. P.

Fedin, Inorg. Chem., 2006, 45, 6950.30 N. K. Al-Rasbi, C. Sabatini, F. Barigelletti and M. D. Ward, Dalton Trans., 2006, 4769.31 J. C. Garrison, M. J. Panzner, P. D. Custer, D. V. Reddy, P. L. Rinaldi, C. A. Tessier and

W. J. Youngs, Chem. Commun., 2006, 4644.32 A. C. G. Hotze, B. M. Kariuki and M. J. Hannon, Angew. Chem., Int. Ed., 2006, 45, 4839.33 J. Xu and K. N. Raymond, Angew. Chem., Int. Ed., 2006, 45, 6480.34 Z. Grote, S. Bonazzi, R. Scopelliti and K. Severin, J. Am. Chem. Soc., 2006, 128, 10382.35 T. B. Jensen, R. Scopelliti and J. C. G. Bunzli, Inorg. Chem., 2006, 45, 7806.36 Q. Sun, Y. Bai, G. He, C. Duan, Z. Lin and Q. Meng, Chem. Commun., 2006, 2777.37 A. Marquis, V. Smith, J. Harrowfield, J.-M. Lehn, H. Herschbach, R. Sanvito, E. L.

Wagner and A. V. Dorsselaer, Chem.-Eur. J., 2006, 12, 5632.38 A.-M. Stadler, N. Kyritsakas, G. Vaughan and J.-M. Lehn, Chem.-Eur. J., 2007, 13, 59.39 S. Yamada, M. Yasui, T. Nogami and T. Ishida, Dalton Trans., 2006, 1622.40 F. Heirtzler, S. Santi, K. Howland and T. Weyhermuller, Dalton Trans., 2006, 4722.41 A. V. Wiznycia, J. Desper and C. J. Levy, Inorg. Chem., 2006, 45, 10034.42 L. Jiang, X. L. Feng, C. Y. Su, X. M. Chen and T. B. Lu, Inorg. Chem., 2007, 46, 2637.43 S. Akine, T. Taniguchi and T. Nabeshima, J. Am. Chem. Soc., 2006, 128, 15765.44 P. Govindaswamy, D. Linder, J. Lacour, G. Suss-Fink and B. Therrien, Chem. Commun.,

2006, 4691.45 Q. Yue, J. Yang, G. H. Li, G. D. Li and J. S. Chen, Inorg. Chem., 2006, 45, 4431.46 J. Zhou, G. Q. Bian, J. Dai, Y. Zhang, Q. Y. Zhu and W. Lu, Inorg. Chem., 2006, 45, 8486.47 J. K. Clegg, L. F. Lindoy, J. C. McMurtrie and D. Schilter, Dalton Trans., 2006, 3114.



48 J. K. Clegg, K. Gloe, M. J. Hayter, O. Kataeva, L. F. Lindoy, B. Moubaraki, J. C.McMurtrie, K. S. Murray and D. Schilter, Dalton Trans., 2006, 3977.

49 R. Murugavel, S. Kuppuswamy, R. Boomishankar and A. Steiner, Angew. Chem., Int. Ed.,2006, 45, 5536.

50 M. S. E. Fallah, F. Badyine, R. Vicente, A. Escuer, X. Solans and M. Font-Bardia, Chem.Commun., 2006, 3113.

51 D. E. Janzen, K. N. Patel, D. G. VanDerveer and G. J. Grant, Chem. Commun., 2006,3540.

52 A. M. Brown, M. V. Ovchinnikov, C. L. Stern and C. A. Mirkin, Chem. Commun., 2006,4386.

53 M. Takeuchi, C. Fujikoshi, Y. Kubo, K. Kaneko and S. Shinkai, Angew. Chem., Int. Ed.,2006, 45, 5494.

54 C.-H. Hung, C.-H. Chang, W.-M. Ching and C.-H. Chuang, Chem. Commun., 2006, 1866.55 G. J. E. Davidson, L. H. Tong, P. R. Raithby and J. K. M. Sanders, Chem. Commun.,

2006, 3087.56 A. S. D. Sandanayaka, Y. Araki, O. Ito, R. Chitta, S. Gadde and F. D’Souza, Chem.

Commun., 2006, 4327.57 S. J. Lee, K. L. Mulfort, J. L. O’Donnell, X. Zuo, A. J. Goshe, P. J. Wesson, S. T. Nguyen,

J. T. Hupp and D. M. Tiede, Chem. Commun., 2006, 4581.58 F. Cheng, S. Zhang, A. Adronov, L. Echegoyen and F. Diederich, Chem.-Eur. J., 2006, 12,

6062.59 R. S. K. Kishore, T. Paululat and M. Schmittel, Chem.-Eur. J., 2006, 12, 8136.60 D. P. Cormode, S. S. Murray, A. R. Cowley and P. D. Beer, Dalton Trans., 2006, 5135.61 T. Ohmura, A. Usuki, K. Fukumori, T. Ohta, M. Ito and K. Tatsumi, Inorg. Chem., 2006,

45, 7988.62 C. G. Oliveri, N. C. Gianneschi, S. T. Nguyen, C. A. Mirkin, C. L. Stern, Z. Wawrzak and

M. Pink, J. Am. Chem. Soc., 2006, 128, 16286.63 F. Hajjaj, Z. S. Yoon, M. C. Yoon, J. Park, A. Satake, D. Kim and Y. Kobuke, J. Am.

Chem. Soc., 2006, 128, 4612.64 B. Botar, P. Kogerler and C. L. Hill, J. Am. Chem. Soc., 2006, 128, 5336.65 H. Zhang, X. Lin, Y. Yan and L. Wu, Chem. Commun., 2006, 4575.66 D.-L. Long, O. Brucher, C. Streb and L. Cronin, Dalton Trans., 2006, 2852.67 N. Fay, V. M. Hultgren, A. G. Wedd, T. E. Keyes, R. J. Forster, D. Leane and A. M.

Bond, Dalton Trans., 2006, 4218.68 M. Kawano, Y. Kobayashi, T. Ozeki and M. Fujita, J. Am. Chem. Soc., 2006, 128, 6558.69 M. W. Heaven, G. W. V. Cave, R. M. McKinlay, J. Antesberger, S. J. Dalgarno, P. K.

Thallapally and J. L. Atwood, Angew. Chem., Int. Ed., 2006, 45, 6221.70 H. Hou, K. C. F. Leung, D. Lanari, A. Nelson, J. F. Stoddart and R. H. Grubbs, J. Am.

Chem. Soc., 2006, 128, 15358.71 C. K. Koo, B. Lam, S. K. Leung, M. H. W. Lam and W. Y. Wong, J. Am. Chem. Soc.,

2006, 128, 16434.72 J.-M. Herrera, M. D. Ward, H. Adams, S. J. A. Pope and S. Faulkner, Chem. Commun.,

2006, 1851.73 X. Yang, B. P. Hahn, R. A. Jones, K. J. Stevenson, J. S. Swinnea and Q. Wu, Chem.

Commun., 2006, 3827.74 D. Braga, S. L. Giaffreda and F. Grepioni, Chem. Commun., 2006, 3877.75 D. Coquiere, J. Marrot and O. Reinaud, Chem. Commun., 2006, 3924.76 B. H. Brodsky and J. D. Bois, Chem. Commun., 2006, 4715.77 M. Pascu, G. J. Clarkson, B. M. Kariuki and M. J. Hannon, Dalton Trans., 2006, 2635.78 M. Albrecht, I. Janser, S. Burk and P. Weis, Dalton Trans., 2006, 2875.79 F. A. Cotton, C. A. Murillo and R. Yu, Dalton Trans., 2006, 3900.80 K. Omata, N. Hoshi, K. Kabuto, C. Kabuto and Y. Sasaki, Inorg. Chem., 2006, 45, 5263.81 L. Metteau, S. Parsons and J. C. Mareque-Rivas, Inorg. Chem., 2006, 45, 6601.82 B. Manimaran, L. J. Lai, P. Thanasekaran, J. Y. Wu, R. T. Liao, T. W. Tseng, Y. H. Liu,

G. H. Lee, S. M. Peng and K. L. Lu, Inorg. Chem., 2006, 45, 8070.83 M. Sathiyendiran, R. T. Liao, P. Thanasekaran, T. T. Luo, N. S. Venkataramanan, G. H.

Lee, S. M. Peng and K. L. Lu, Inorg. Chem., 2006, 45, 10052.84 Y. B. Dong, T. Sun, J. P. Ma, X. X. Zhao and R. Q. Huang, Inorg. Chem., 2006, 45,

10613.85 D. Fiedler, H. vanHalbeek, R. G. Bergman and K. N. Raymond, J. Am. Chem. Soc., 2006,

128, 10240.86 X.-P. Zhou, D. Li, T. Wu and X. Zhang, Dalton Trans., 2006, 2435.87 C.-D. Wu and W. Lin, Dalton Trans., 2006, 4563.



88 S. P. Argent, H. Adams, T. Riis-Johannessen, J. C. Jeffery, L. P. Harding, W. Clegg, R. W.Harrington and M. D. Ward, Dalton Trans., 2006, 4996.

89 C. S. Liu, P. Q. Chen, E. C. Yang, J. L. Tian, X. H. Bu, Z. M. Li, H. W. Sun and Z. Lin,Inorg. Chem., 2006, 45, 5812.

90 B. Zhai, L. Yi, H. S. Wang, B. Zhao, P. Cheng, D. Z. Liao and S. P. Yan, Inorg. Chem.,2006, 45, 8471.

91 J. Sun, Y. Zhou, Q. Fang, Z. Chen, L. Weng, G. Zhu, S. Qiu and D. Zhao, Inorg. Chem.,2006, 45, 8677.

92 S. Noro, R. Kitaura, S. Kitagawa, T. Akutagawa and T. Nakamura, Inorg. Chem., 2006,45, 8990.

93 L. Song, J. Li, P. Lin, Z. Li, T. Li, S. Du and X. Wu, Inorg. Chem., 2006, 45, 10155.94 R. M. Silva, C. Gwengo, S. V. Lindeman, M. D. Smith and J. R. Gardinier, Inorg. Chem.,

2006, 45, 10998.95 S. Masaoka, D. Tanaka, H. Kitahata, S. Araki, R. Matsuda, K. Yoshikawa, K. Kato, M.

Takata and S. Kitagawa, J. Am. Chem. Soc., 2006, 128, 15799.96 J. He, Y.-G. Yin, T. Wu, D. Li and X.-C. Huang, Chem. Commun., 2006, 2845.97 A. Galet, M. C. Munoz and J. A. Real, Chem. Commun., 2006, 4321.98 D.-R. Xiao, E.-B. Wang, H.-Y. An, Y.-G. Li, Z.-M. Su and C.-Y. Sun, Chem.-Eur. J.,

2006, 12, 6528.99 M.-H. Zeng, X.-L. Feng, W-X. Zhang and X.-M. Chen, Dalton Trans., 2006, 5294.



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